Well, your point is clear, computer-defence is needed.
Ofcource it is needed, but he.
I quote
If you have internet access without a good firewall for half an hour or more you can expect anything to get messed up inside your computer.
You say just the acess to internet for half an hour could break a computer, let I just say that my computer was todat for something like a few hours completely unprotected, nothing no virus-scanner no firewall anything, I stopped any program from starting up to check the network-problems. I have forget to put them on, your speech inmidatly made me put it back on.
And the teenage girl you describe looks awful much like my sister, she hasn't got any problems, atleast she doesn't say she have. Maybe do a little scan on her computer, it wouldn't suprise me if it was serious infected.
Edit:
Testlund have you checked a internet port-scanner, with that many port-scans it seems to me they aren't like they call it 'stealth'. So it can be seen there is a computer a the IP, and the scans are being done to attack if the configuration has changed and a port is unblocked.